1. Technical Field
The present invention relates to a method for manufacturing an optical element, a method for manufacturing a projector, an optical element and a projector.
2. Related Art
In a projector having a liquid crystal device as an optically modulating device, a polarization plate is disposed in at least one of a light-incident side and a light-emission side of the liquid crystal device. The polarization plate that is a two or three-layered lamination, having a polarization layer comprising polyvinyl alcohol (PVA) and at least one supporting layers comprising triacetyl cellulose (TAC) laminated in one side or both sides of the PVA for purpose of enhancing mechanical strength thereof is a well-known example of the polarization plate (see JP-A-7-20317). The supporting layer comprising TAC is excellent in transparency, uniformity and planarity and has very little anisotropic. Accordingly, the supporting layer comprising TAC is widely used for a supporting layer in order to support the polarization layer.
Meanwhile, in a projector of a related art, a light that does not pass through the polarization plate gives rise to an increase in temperature of the polarization plate because the light is absorbed in the polarization plate to generate a considerable amount of heat. Consequently, the projector of the related art has some disadvantages such that a display quality of a projection image is lowered. For example, the polarization characteristics of the polarization plate are deteriorated, the contrast of the projection image is lowered, and an uneven contrast or an uneven color is generated.
Therefore, a projector having an optical element comprising a light transmissive member having a thermal conductivity that is adhered to both sides of the polarization plate (namely, outer surface of the supporting layer of the polarization plate) is provided in order to solve the problem of the projector of the related art (see JP-A-2000-112022). In the projector, the heat generated in the polarization plate is emitted outside of the projector through the light transmissive member having a thermal conductivity so that the increase of the temperature of the polarization plate may be avoided. Therefore, the deterioration of the polarization plate may be prevented and accordingly, the polarization characteristic of the polarization plate may not be lowered. Accordingly, a projector having the optical element may enhance the display quality of the projection image.
Meanwhile, recently, the demand for a projector for use in electric home appliances having a projector, such as a home theater system is increased. Consequently, it is more required for the projector to have an improved quality of the projection image. However, in a projector of a related art, which uses a material having an optical axis as a light transmissive member having a thermal conductivity, the polarization state of a light which passes through the light transmissive member and is incident on the polarization plate or the polarization state of a light which passes through the polarization plate and is incident on the light transmissive member may be varied if an optical axis of the light transmissive member and a polarization axis of the polarization plate do not have a desired positional relationship therebetween. Accordingly, the contrast of the projection image may be decreased, and the temperature of the polarization plate may be increased so that the display quality of the projection image is lowered. In addition, in the projector of the related art, an incident side polarization plate is disposed on a light-incident side of the liquid crystal device and an emission side polarization plate is disposed on a light-emission side of the liquid crystal device, in order that the incident side polarization plate and the emission side polarization plate are in a so-called crossed Nicols state. Herein, if the incident side polarization plate and the emission side polarization plate are not placed in an optimal rotational position, the contrast of the projection image may be decreased, or the temperature of the emission side polarization plate may be increased so that the display quality of the projection image is lowered.